Two-part implant with a hydroxylated soft tissue contact surface

ABSTRACT

Two-part implant for attachment of artificial teeth comprising a base body having a bone contact surface and a soft tissue contact surface. The soft tissue contact surface is at least partially hydroxylated or silanated which results in an improved soft tissue integration.

RELATED APPLICATIONS

This application is a divisional of and claims priority under 35 U.S.C.§120 to U.S. Ser. No. 11/680,055, filed Feb. 28, 2007, which claimspriority to European Application No. 06004063.1, filed Feb. 28, 2006,the disclosures of which are incorporated herein in their entirety byreference.

FIELD OF THE INVENTION

The present invention relates to a two-stage implant comprising a basebody having a bone contact surface and a tissue contact surface and to amethod for preparing such an implant.

BACKGROUND

Implants which are used for insertion into bone, for example forattachment of artificial teeth, are known per se. Different types ofimplant systems are known, for example two-part implant systems. Saidtwo-part implant systems comprise first an anchoring part for anchoringwithin the bone and second a mounting part. Onto the mounting partprosthesis elements, such as bridges or crowns, are screwed or cementedusually using intermediate so-called abutments.

A central property of said implants is their osteointegration time, thatis to say the time that passes before the bone substance has becomeconnected with sufficient strength and permanently to the bone contactsurface, that is to say it has become integrated with it.

Therefore, much effort has been made in order to improve theosteointegration of said implants, such as described in EP 1 150 620. Itwas shown that the osteointegration time was significantly shorter ifthe bone contact surface of the implant is roughened, hydroxylated andhydrophilic.

US 2004/0049287 discloses an endosseous implant, said implant having asurface made from metal or ceramic. The surface has a smooth or roughtexture and has been treated with at least one pharmaceuticallyacceptable organic compound carrying at least one phosphonic acid group.Said implants showed an improved bone bonding strength.

U.S. Pat. No. 5,397,362 discloses an implant prosthesis comprising asubstrate of a ceramic material, a glass layer coated over the adheringinterface of the substrate and a thermally sprayed layer of calciumphosphate based material formed over the glass layer.

WO 2005/120386 discloses a dental implant comprising an anchoringelement for anchoring the dental implant in the bone and an abutment forfastening a crown or the like suprastructure. The anchoring element andthe abutment are produced from zirconium oxide.

However, there is considerable evidence supporting the view that thesupracrestal connective tissue plays a fundamental role in establishingan effective seal between the oral environment and the endosseous partof a dental implant. Indeed, the presence of bacteria on the implantsurface may lead to an inflammation of the peri-implant mucosa, and, ifleft untreated, the inflammation spreads apically and results in boneresorption. As a consequence of the fact that rough surfaces accumulateand retain more plaque than smooth surfaces, nowadays, the soft tissuecontact surface of the implants is highly polished (see OralImplantology, Thieme Verlag, 1996, page 438).

Various experiments have been carried out to investigate the differenceof early inflammatory response to mucosa-penetrating implants preparedwith varying surface roughness. Despite the fact that a rough surfacemay accumulate greater amounts of plaque than a smooth surface, norelation was found between inflammatory response and implant surfaceroughness (Wennerberg et al, J. Clin. Periodontol 2003: 30: 88-94;Quirynen et al, The International Journal of Oral and MaxillofacialImplants, 11, No. 2, 1996).

It is the problem of the present invention to provide an implant withimproved soft tissue integration.

SUMMARY OF THE INVENTION

An implant according to the invention comprises a base body having abone contact surface and a soft tissue contact surface, wherein the softtissue contact surface is at least partially hydroxylated or silanated.Said soft tissue contact surface has the potential to promote formationof soft tissue attachment. In contrast to conventional implants having aroughened, in same cases also hydroxylated bone contact surface and asmooth unhydroxylated tissue contact surface, the implant according tothe present invention leads to the formation of new connective tissueadjacent to the soft tissue contact surface of the implant and the newconnective tissue tends to be in close contact with the soft tissuecontact surface of the implant. The loose connective tissue seems tobecome organized and replaced be newly formed collagen fibers,originating from its outer zone. These fibers tend to be organized in aperpendicular way towards the soft tissue contact surface, similarly tothe naturally occurring fibers most responsible for compensation forceson the tooth.

An implant in terms of the present invention is intended to mean theanchor part of a two-part implant system, that is that part whichbecomes integrated with the bone. The anchoring part of said two-partimplant system may be inserted in a one-stage or a two-stage procedure.Said anchoring part is sunk in up to about 1.5-3 mm above the bone ridgeat mucosal level. Said anchor part has a bone contact surface meaningthe part which is in contact with the bone. The top of the anchoringpart which is in contact with the soft tissue is defined as the softtissue contact surface. After implantation the wound edges can bedirectly adapted to the soft tissue contact surface thereby effecting aprimary soft tissue closure to the implant.

“Hydroxylated” in terms of the present invention means hydroxyl groupswhich are present in the outermost atomic layer of the implant surface.If the implant comprises titanium, zirconium, tantalum, niobium, hafniumor alloys thereof as well as chemically similarly reacting alloys, it isassumed that the surface of metal oxidizes spontaneously in air andwater and that a reaction then takes place with water on the surface toform hydroxyl groups. This surface containing hydroxyl groups isreferred to in the literature as a “hydroxylated” surface; cf. H. P.Boehm, Acidic and Basic Properties of Hydroxylated Metal Oxide Surfaces,Discussions Faraday Society, vol. 52, 1971, pp. 264-275. The sameapplies to ceramic surfaces (either on a ceramic implant or a metallicimplant with a ceramic coating). A metal surface whose hydroxyl groupsare covalently blocked, e.g. because of chemical modification, is not a“hydroxylated” surface in terms of the present invention.

Silanated in terms of the present invention means that the implantsurface is covered by a silanole or by an organo silane compound whichhas at least one free hydroxyl group. Examples of such organo silanecompounds are X_(n)SiR_(4-n), wherein X is selected from the groupconsisting of Cl, Br, I, F or OR, and R is selected from the group oflower alkyl groups, such as methyl, ethyl, propyl etc. Implants made ofmetal are preferably covered by a silanole, whereas implants made ofceramic are preferably covered by an organo silane compound. Implantsmade of metal can also be covered by an organo silan compound, andimplants made of ceramic can also be covered by silanole.

In a preferred embodiment of the present invention the soft tissuecontact surface is completely hydroxylated. Such an implant showed goodresults in vivo and said implants are economically interesting and canbe produced in a controlled process. In addition it has been shown thatwith the implants according to the present invention the healing processis improved, that is a good osteointegration as well as an excellentsoft tissue integration is achieved. Therefore, the implants comprise areduced risk of periimplantitis and as a consequence fewer implants willhave to be replaced. Due to their purity, meaning that the soft tissuecontact surface is free of organic compounds, the surface charge isbetter available. Therefore, the surface is hydrophilic, which resultsin an improved soft tissue integration. Therefore, they do not bear therisk of autoimmune reactions and other unwanted side effects.

In a further embodiment of the present invention the soft tissue contactsurface is roughened and hydroxylated. A roughened surface in terms ofthe present invention means a macroscopic texture of the surface whichis obtained for example by sandblasting the soft tissue contact surface.It has been found that if the soft tissue contact surface is roughenedand hydroxylated the blood coagulum is stabilized which accelerates thehealing procedure.

In a further embodiment of the present invention the soft tissue contactsurface is smooth but hydroxylated. A smooth surface in terms of thepresent invention means a macroscopic texture of the surface which isobtained for example by machining or additional polishing, preferably byelectropolishing the soft tissue contact surface. With a smooth surfacethe accumulation of plaque can be prevented or at least minimized, andsuch a soft tissue contact surface has outstanding wettabilityproperties which is highly preferred.

In a further embodiment of the present invention the bone contactsurface and the soft tissue surface of the implant are both roughened,hydroxylated and hydrophilic or alternatively both smooth, hydroxylatedand hydrophilic. Such implants are particularly easy to produce sincethe entire implant can be treated in the same way. This is a very bigadvantage and is based on the surprising finding that a hydroxylated,hydrophilic and roughened soft tissue surface of the implant showsimproved soft tissue integration.

In a further preferred embodiment of the present invention the softtissue contact surface is hydrophilic. In terms of the presentinvention, the soft tissue contact surface is referred to as“hydrophilic” if it is freely accessible to the body fluid and notcovered with foreign substances, for example substances with ahydrophobic action. Various volatile hydrocarbons are conventionallypresent in non-purified air. These are rapidly adsorbed in a thin layerby hydroxylated and hydrophilic surfaces, whereby such surfaces are nolonger hydrophilic. Likewise, such a hydroxylated and hydrophilicsurface can become hydrophobic if the hydroxyl groups present on thesurface associate or react chemically e.g. with carbon dioxide presentin the air or with organic solvents, such as methanol or acetone,introduced via the cleaning process. The hydrophilic properties of thesoft tissue contact surface may result in a higher wettability whencompared to an untreated soft tissue contact surface, which promotesformation of the soft tissue. Further, the charge on the surface isbetter available which may accelerate the formation of soft tissueattachment as well.

The implants according to the invention preferably comprise mainly ametal selected from the group consisting of titanium, zirconium,niobium, hafnium or tantalum, preferably titanium or zirconium.Alternatively the implants comprise an alloy of metals selected from thegroup consisting of titanium, zirconium, niobium, hafnium or tantalum,preferably a binary titanium/zirconium alloy. Such implants, theirnature and the metal materials used to produce them are known per se andare described for example in J. Black, G. Hastings, Handbook ofBiomaterials Properties, pages 135-200, published by Chapman & Hall,London, 1998. From an aesthetic point of view, in particular in thefront visible region, the soft tissue contact surface is preferablycovered with a ceramic coating. This is for example obtainable bythermally spraying a ceramic material on the surface of a metallic corematerial such as described in U.S. Pat. No. 4,746,532. Also EP 1 566 152describes the coating of a dental implant with zirconia. Alternativelythe implants may comprise a ceramic ring element, in particular in thesoft tissue contact surface. Such ceramic coatings and ring elementscomprise typically zirconia, aluminia, silica or mixtures thereof withpossible further constituents, preferably they are made of zirconia.Alternatively the implant according to the present invention may be madeof ceramic.

In a most preferred embodiment the implant according to the presentinvention is made of ceramic comprising a zirconium oxide basedmaterial. The cubic structure of zirconium oxide (zirconia) may bestabilized by metallic oxides at room temperature. Preferred metallicoxides are magnesium oxide, calcium oxide, oxides of the lanthanidegroup, preferably yttrium oxide. Depending on the content of saidmetallic oxides the cubic high temperature phase of zirconia can bestabilized fully or partly at room temperature (cubic stabilizedzirconium oxide). Preferably zirconia is stabilized by yttrium oxide.

The present invention also relates to the process for preparing theabove disclosed implant.

To obtain the hydroxylated surface, the soft tissue contact surface ofthe implant is preferably etched with an inorganic acid, an inorganicbase, a mixture of inorganic bases or a mixture of inorganic acids.Particularly preferred are inorganic acids such as hydrofluoric acid,hydrochloric acid, sulfuric acid, nitric acid or a mixture of suchacids. Preferably the implant is etched with a mixture of hydrochloricacid (conc.), sulphuric acid (conc.) and water in a weight ration ofabout 2:1:1. Alternatively the surface is activated with hydrochloricacid (conc.), hydrogen peroxide (conc.) and water in a weight ratio ofabout 1:1:5. The soft tissue contact surface is then washed with purewater in an inert atmosphere.

A roughened soft tissue contact surface can be obtained by sandblastingsaid surface and keeping the surface in the resulting state if it isalready hydroxylated and hydrophilic or converting the sandblastedsurface to a hydroxylated and hydrophilic state in a separate processstep.

In particular, the roughened soft tissue contact surface can be producedby shot peening or sandblasting said surface and/or roughening it byusing plasma technology, and then treating the mechanically roughenedsurface by an electrolytic or chemical process until a hydroxylated andhydrophilic surface is formed.

The preferred procedure is to

-   -   shot-peen the soft tissue contact surface of the implant and        then etch it with diluted hydrofluoric acid at room temperature;        or    -   sandblast the soft tissue contact surface of the implant, e.g.        with aluminium oxide particles having a mean size of 0.1-0.25 mm        or 0.25-0.5 mm, and then treat it at elevated temperature with a        hydrochloric acid/sulfuric acid mixture and wash it with pure        distilled and carbon-free (CO₂ and other carbons) water; or    -   sandblast the soft tissue contact surface of the implant with        coarse particles, e.g. with a mixture of particles as defined        above, and then treat it with a hydrochloric acid/nitric acid        mixture and wash it with pure distilled and carbon-free (CO₂ and        other carbons) water; or    -   treat the soft tissue contact surface of the implant with a        mixture of hydrochloric acid (conc.), hydrogen peroxide (conc.)        and water in a weight ratio of about 1:1:5 and wash it with pure        distilled and carbon-free (CO₂ and other carbons) water; or    -   roughen the soft tissue contact surface by using plasma        technology and then hydroxylate it in a mixture of hydrochloric        acid (conc.), hydrogen peroxide (conc.) and water in a weight        ratio of about 1:1:5 and wash it with pure distilled and        carbon-free (CO₂ and other carbons) water; or    -   treat the soft tissue contact surface by an electrolytic        process, optionally after mechanical roughening of the surface,        and then wash it with pure distilled and carbon-free (CO₂ and        other carbons) water; or    -   treat the soft tissue contact surface of the implant by plasma        cleaning or UV-treatment.

These methods are known to those skilled in the art and are describedfor example in U.S. Pat. No. 5,071,351, The hydroxylated soft tissuecontact surface of the implant is after such a treatment free of organicdebris and has increased wettability. As a result, the implant becomesmore intimately involved with the surrounding bone and tissue structure.

Whatever the case may be, according to the invention the implant is notsubjected to further aftertreatment, i.e. it is not treated withalcohol, acetone or any other organic solvent. In particular, said purewater contains neither carbon dioxide nor hydrocarbon vapours andespecially no acetone and no alcohols like methanol or ethanol. However,it can contain special additives as described below. The “pure” waterused for washing has preferably been distilled several times or preparedby reverse osmosis; the water has preferably been prepared in an inertatmosphere, i.e. under reduced pressure in a nitrogen or noble gasatmosphere, for example.

Following these procedures, the implant 1 obtained is left in pure waterand stored in a closed vessel or a covering 2, as shown in FIG. 2. Inaddition to water, the interior of the covering can contain inert gases3, for example nitrogen, oxygen or a noble gas such as argon. Theimplant obtained is preferably stored in pure water optionallycontaining selective additives, and in a covering which is practicallyimpermeable to gases and liquids, especially to carbon oxides, theinterior of the covering being devoid of any compounds capable ofimpairing the activity of the implant surface.

Alternatively, the implant could be placed in an inert gas atmosphere.

The implant according to the invention, or at least its hydroxylated andhydrophilic surface, is preferably sealed in a gas-tight andliquid-tight covering, the interior of the covering being devoid of anycompounds capable of impairing the biological activity of the implantsurface. In this way it is avoided that the surface loses its activationfully or partially by means of air constituents, before the dentalimplant is applied. In a preferred embodiment there is a reducingatmosphere in the interior of the covering. This gas-tight andliquid-tight covering is preferably a heat-sealed ampoule made of glass,metal, a synthetic polymer or some other gas-tight and liquid-tightmaterial, or a combination of these materials. The metal preferablytakes the form of a thin sheet, it being possible for polymericmaterials and metal sheets, as well as glass, to be combined together toform a suitable packaging in a manner known per se.

Examples of suitable additives which can be incorporated in the purewater are cations and anions which already occur in the body fluid. Inorder to stabilize the positive charge the implant according to thepresent invention is preferably stored at a pH ranging from pH 3 to 7,preferably 4 to 6. Alternatively it is also possible to store theimplant at a pH ranging from pH 7 to 10 in order to stabilize thenegative charge. Preferred cations are Na⁺, K⁺, Mg²⁺ and Ca²⁺. Thepreferred anion is Cl⁻. The total amount of said cations or anionsranges preferably from about 50 mM to 250 mM, particularly preferablyfrom about 100 mM to 200 mM, and is preferably about 150 mM. If thecovering contains divalent cations, especially Mg²⁺, Ca²⁺, Sr²⁺ and/orMn²⁺, on their own or in combination with the above-mentioned monovalentcations, the total amount of divalent cations present preferably rangesfrom 1 mM to 20 mM.

The invention is explained below on the basis of figures andillustrative embodiments, without in any way limiting the invention tothe embodiments shown.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the different areas of an embodiment of an implantaccording to the invention that is the anchoring part of a two-partimplant system.

FIG. 2 shows an implant system according to the invention.

DETAILED DESCRIPTION

In accordance with one embodiment of the invention, FIG. 1 shows animplant 1 which is preferably made of a tissue compatible metal or of analloy of such a metal, in particular of titanium or of a titanium alloy.Alternatively the implant is made of ceramic, preferably of zirconia.Further it is possible that parts of the implant are made of metal andparts of the implant are made of ceramic, for example if the inner partis made of titanium and the outer part of the implant is made ofceramic. The implant 1 has a threaded section 10 and a rounded lower end15. At its upper end it has a slightly enlarged conical section 20. Saidimplant 1 is subdivided into a bone contact surface B and a soft tissuecontact surface S. In the boundary area of these surfaces, there is atransition area B/S from bone contact surface B to soft tissue contactsurface S, which transition area is assigned to both aforementionedareas. The question of whether this area, in the implanted state, islocated in the bone or in the soft tissue depends on a large number offactors, for example the depth to which the implant is screwed, thetissue reaction, etc. The transition area has to be treated in the sameway as the bone contact surface, in order to make sure, that in any casean optimal osteointegration is ensured. In the case of implants 1 madeof titanium, the bone contact surface is preferably roughened, and evenmore preferred hydroxylated and hydrophilic as well. The soft tissuecontact surface S is at least partially, preferably completelyhydroxylated. In a preferred embodiment it is also roughened and/orhydrophilic. The soft tissue contact surface of an implant according tothe present invention may be made of titanium, zirconium, tantalum,niobium, hafnium or alloys thereof as well as chemically similarlyreacting alloys, but it is also possible that the implant has a ceramiccoating which is hydroxylated.

The Examples which follow illustrate the invention.

Example 1 Implant with a Roughened Hydroxylated Soft Tissue ContactSurface

A common shape of dental implant in the form of a screw of diameter 4 mmand length 10 mm was produced. The crude shape was obtained in a mannerknown per se by removing material from the cylindrical blank by turningon a lathe and milling. The bone contact surface as well as the softtissue surface were then sandblasted with particles having a mean sizeof 0.25-0.5 mm as described in EP 0 388 575. The roughened surface wasthen treated for about five minutes at a temperature above 80° C. withan aqueous hydrochloric acid (conc.)/sulfuric acid (conc.) mixturehaving an HCl:H₂SO₄:H₂O ratio of 2:1:1. The implant formed in this waywas washed with pure water and then heat-sealed directly in a glassampoule filled with pure water containing 150 mM Na⁺ ions, and thecorresponding amount of Cl⁻ anions.

To test the soft tissue integration, the above implants were placed infour female fox hounds. Each animal received 6 implants bilaterally inthe upper jaw and 10 implants bilaterally in the lower jaw. The implantswith a roughened hydroxylated soft tissue contact surface showedunexpectedly a much better soft tissue integration than comparableimplants with an unhydroxylated surface. Soft tissue adhesion was seenalready after a few days, the soft tissue integration was apparentwithin two weeks.

Example 2 Implant with a Smooth Hydroxylated Soft Tissue Contact Surface

A common shape of dental implant in the form of a screw of diameter 4 mmand length 10 mm was produced. The crude shape was obtained in a mannerknown per se by removing material from the cylindrical blank by turningon a lathe and milling. The bone contact surface was then sandblastedwith particles having a mean size of 0.25-0.5 mm, whereas the softtissue contact surface has been electropolished. The sandblasted bonecontact surface as well as the electropolished soft tissue contactsurface were then treated for about five minutes at a temperature above80° C. with an aqueous hydrochloric acid (conc.)/sulfuric acid (conc.)mixture having an HCl:H₂SO₄:H₂O ratio of 2:1:1. The implant formed inthis way was washed with pure water and then heat-sealed directly in aglass ampoule filled with pure water containing 150 mM Na⁺ ions, and thecorresponding amount of Cl⁻ anions.

To test the soft tissue integration, the above implants were placed infour female fox hounds. Each animal received 6 implants bilaterally inthe upper jaw and 10 implants bilaterally in the lower jaw. The implantswith a smooth hydroxylated soft tissue contact surface showedunexpectedly a much better soft tissue integration than comparableimplants with an unhydroxylated surface. Soft tissue adhesion was seenalready after a few days, the soft tissue integration was apparentwithin two weeks.

What is claimed is: 1-19. (canceled)
 20. Anchor part of a two-partimplant system for attachment of artificial teeth, the anchor part beingmade of ceramic and comprising a base body having a bone contact surfaceand a soft tissue contact surface, wherein the soft tissue contactsurface is at least partially hydroxylated.
 21. Anchor part according toclaim 20, wherein the soft tissue contact surface is completelyhydroxylated.
 22. Anchor part according to claim 20, wherein the softtissue contact surface is roughened.
 23. Anchor part according to claim20, wherein the soft tissue contact surface is smooth.
 24. Anchor partaccording to claim 22, wherein the surface roughness of the soft tissuecontact surface increases towards the bone contact surface continuouslyor stepwise.
 25. Anchor part according to claim 20, wherein the softtissue contact surface is hydrophilic.
 26. Anchor part according toclaim 20, wherein the soft tissue contact surface has the samemacroscopic texture as the bone contact surface.
 27. Anchor partaccording to claim 20, wherein it is made of ceramic comprising azirconium oxide based material.
 28. Method for producing an anchor partof a two-part implant system in accordance with claim 20, wherein thesoft tissue contact surface is treated with a chemical etching procedureuntil a hydroxylated surface has been produced.
 29. Method according toclaim 28, wherein the soft tissue contact surface is shot-blasted,sandblasted and/or roughened using plasma technology before treatingwith the chemical etching procedure.
 30. Method according to claim 28,wherein the chemical etching procedure is carried out with an inorganicacid or a blend of inorganic acids.
 31. Method according to claim 30,wherein said inorganic acid is selected from the group consisting ofhydrofluoric acid, hydrochloric acid, sulphuric acid and mixturesthereof.
 32. Method according to claim 30, wherein said blend ofinorganic acids is hydrochloric acid (conc.), hydrogen peroxide andwater in a weight ratio of approximately 1:1:5.
 33. Method according toclaim 30, wherein said blend of inorganic acids is a mixture ofhydrochloric acid (conc.)/sulphuric acid (conc.)/water: 2/1/1. 34.Method according to claim 28, wherein the surface is washed with purewater, which can additionally comprise additives, in an atmosphere thatis inert in relation to the surface, and the surface, without subjectionto a further treatment, is stored in an atmosphere that is inert inrelation to the anchor part surface, and/or constantly in the presenceof pure water, which can comprise additional additives.
 35. Gas-tightand liquid-tight covering containing the anchor part according to claim20.
 36. Method according to claim 34, wherein the surface is stored in acovering which is impermeable for gases and liquids.